Guard your free time from unnecessary stress. If you want your free time to be truly useful, don't allow non-free time things to bleed into it. The reason for this is that your free time is needed to refresh you and improve your energy, your creativity, and your sense of self. If you let the usual mundane activities of everyday life creep into your free time under the pretense of being "useful," you won't gain anything from your free time and you will have very loose boundaries between free time and the rest of your time, thereby devaluing your free time.